Thermostatic element



Jan. 13, 1948. P. s. CHACE w 2,434,392

Patented Jan. 13, 1948 2.434.392 'rnEaMos'rA'rrc ELEMENT Paul G. Chace,Attleboro Falls, Masa, assignor to Metals & Controls Corporation,

Attleboro,

Mass, a corporation of Massachusetts Application Gctober 9, 1943, SerialNo. 505,829 1 Claim. (Cl. 29-1913) or cold-worked wire element havingdesired mechanical rigidity with more thermal flexibility than has beenobtained heretofore in such wires: and the provision of an element ofthe class described whichis simple and economical to manufacture. Otherobjects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations ofelements, features of construction, and arrangements of parts which willbe exemplified in the structures hereinafter described, and the scope ofthe application of which will be indicated in the following claim.

In the accompanying drawings, in which is illustrated one of variouspossible embodiments of the invention,

Fig. 1 is an enlarged cross section oi. an old form of finished wire,shown for purposes of illustrating remarks made hereinafter;

Fig. 2 is an enlarged cross section of my new form of wire; and,

Fig. 3 is a fragmentary view. on a reduced seal of a typical ingot fromwhich wire is cold-worked.

Similar reference characters indicate corresponding parts throughout theseveral views of the drawings,

Heretofore bimetallic elements for thermostatic and similar uses havebeen made in various cross sections and have been composed ofvariousmaterials bonded together throughout their adjacent surfaces, as byfusing. hard soldering,

etc. Included in these prior-art constructions were cold-drawnbimetallic wire made for example of brass and Invar components; Themethod of making such a wire was to form a bonded bimetallic ingot suchas shown in Fig. 3, and then to cold work this down into wire form ofthe desired diameter and shape oi cross secupon circumstances it wouldhave a variety of shapes. In Fig. 1, numeral l indicates in general theold form of cold-worked bimetallic wire. Numeral 3 indicates a brasscomponent and numeral 5 a bonded Invar component.

The reason for this prior-art characteristic wavy line or surface I 3between the cold-worked bimetallic components was that the metalsemployed (brass and Invar for example) did not have the samework-hardening rates throughout the whole work-hardening range. Thus onewould become harder than the. other during the work-hardening operationsand distort the other at or near the bonded junction between the metals.1

Another resulting disadvantage of the prior structure is that the wavyjuncture between elements tends to stiffen the wire around the neutralaxis indicated by dash lines, particularly in its bending responses totemperature changes.

The present invention avoids the wavy juncture and produces one that ispractically a straight line, H, as shown in Fig. 2. This is done bychoosing a combination of metal elements, each of which hassubstantially the same workhardening rate.- For example, a satisfactorycombination of elements is silicon-bronze and Invar, the bronze beingconstituted by approximately 98% copper, 1.5% silicon and 0.5% manganese(all by weight). The Invar contains (by weight) approximately 36%nickel, together with about 0.05% of carbon and 0.5% of manganese. Thecombination of these materials bonded in an ingot similar to the oneshown in Fig. 3 and hot or cold worked by rolling or drawing down to thedesired wire section will result in a wire such as shown at l in Fig. 2.In this case 9 represents I the silicon-bronze component, and 5 theInvar Fig. 1, for example. It'is not to be understood that the wave formshown in Fig. 1 is always that which would be assumed, and thatdepending 56 component, both bonded at junction H. Compared to thejunction l3 shown in Fig. l, junction II is quite straight and flat.

The thermal activity, for a given weight of wire, in the case of theconstruction shown in Fig. 1 averages of the order of 20 to 25% lessthan that shown in the construction 01' Fig. 2. This is because of thediiference in the geometric character 01' the bonding surface in thefinal wire. In the improvements shown in Fig. 2, the two metalcomponents exert more or less equal stresses on each other throughoutthe coldworking operation which results in the straightline bond.

Another advantage of the invention is that the tendency to split the twometal components apart at or nea'r the bond is much reduced by thestraight-line juncture. In the prior-art wire, shown in Fig. 1, evenwith proper bonding between the components 3 and 5 the uneven drawing:tresses exerted upon the uneven juncture ten to cause splitting. Thistrouble is practically eliminated in the improved form 01 the invention(Fig. 2).

It is of course understood that a characteristic such as straightness isrelative and that. due to processing errors and other unavoidableexigencies, a bond line in an article made according to the inventionmight deviate minutely from a straight line, but from a practicalviewpoint it will be insubstantial.

The drawings are diagrammatic. In practice the wavy form of the junctureshown in Fig. 1 may take up any of various curvatures, depending uponlocal conditions.

Although the .drawings show the bond lines about central, they may beoffset to one side, if this should be found desirable. Thus a chordwould be formed by line H, instead of a diameter as shown ,in Fig. 2.Regardless of where the bond line is to the section of the thermostaticelement, it is substantially straight and incorporates the advantagesset forth herein. It will be understood that although the principles ofthe invention have been described in connection with a bimetallic wirethey would likewise apply to wires having more than two diflerentmetallic components.

It is realized that heretofore bimetallic elements have been, made upfrom sheet-like components which produced composite thermostaticelements having more or less straight line junctions between thecomponents. But these were not drawn elements, such as contemplated bythe present invention, and in which the problem solved arises. It is thecold-working operation that causes the difficulties solved. Theinvention is not limited,

except where limited in the claims, to any Particular cross section ofwire becaus many diflerent sections can be stretched into shape. It isnoteworthy however that the circular shape of wire,

' 4 during prior-art cold-working, produces quite a wavy bond.

Another advantage oi a combination of materials as described is thattheir similar working properties allows the combination to be reduced byprocesses of hot working.

In view of the above, it will be seen that the several objects oi theinvention are achieved and other advantageous results attained.

As many changes could be made in the above constructions withoutdeparting irom the scope of the invention, it is intended that, allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

I claim:

A bimetallic wire having a substantially flat bond, the bimetalliccomponents oi which consist respectively of silicon-bronze containingapproximately 98% copper, 1.5% silicon and 0.5% manganese by weight, andInvar containing approximately 36% nickel, 0.05% carbon, 0.5% manganeseby weight and the'remainder iron.

* PAUL G. CHACE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,125,858 Hood Aug. 2, 1938791,698 Jett June 6, 1905 1,813,122 Mo'ore July 7, 1931 1,936,397Jennison Nov. 21, 1933 1,947,065 Scott Feb. 13, 1934 1,948,121 MatthewsFeb. 20, 1934 2,162,524 Brace June 13, 1939 2,279,105 Boettinger Apr. 7,1942 2,327,500 Chace Aug. 24, 1943 OTHER REFERENCES American Machinist.August 23, 1939, pages 646, 647.

